"We're still hard at work on the GDK, but in the meantime, you can start designing and developing your awesome ideas with the existing Android SDK," suggests the post.

"Although you won't have all the tools necessary to design the perfect experience for Glass, developing with the Android SDK (API Level 15) lets you try out ideas while you wait for the GDK."

The team add that Glass features including the accelerometer and playing media are already part of the Android SDK. Google has published some sample apps including a stopwatch, level and compass for Glass, with more to come in the next few weeks.

"When we release the GDK, we'll update these samples to demonstrate the migration path between a traditional Android app and a full Glass experience," explains the blog post.

In fact, a number of companies and developers have already released third-party Glass apps, either through working with Google ahead of the GDK's launch, or by using its Google Mirror API for web-based Glassware.

Meanwhile, e-commerce service Fancy has a Glass app enabling people to take photos of objects in the world around them then find matching products, and cloud-storage service Evernote have also released a "first look" at its app.

Fancy's Glass app helps people find colour-matched products PR

All have stressed that it is early days for their apps on Glass, even if they have grand ambitions.

"We believe that wearables are the next frontier in consumer technology and we're hard at work building the Evernote for our wearable technology future," as that company's vice president of marketing Andrew Sinkov put it in a blog post.

"Today, you're getting a glimpse of simple and useful ways that Evernote can be used with Google Glass. This is only the beginning."

It includes rules on collecting and using people's personal data, as well as barring sexually explicit material, depictions of "gratuitous" violence, hate speech, impersonation and deceptive behaviour, gambling and malware, among other categories.